The present invention relates to methods and apparatus for engine testing in the automotive industry, and more particularly, to timing lights used in conjunction with engine scope testers.
Engine scope testers are being used more and more for the repair and maintenance of automotive engines. Such devices provide a capability for engine analysis and ignition adjustment far in excess of that possible without their use. In particular, the setting of the distributor position to provide spark plug firings at the correct point relative to engine rotation as specified by the manufacturers can be done in an accurate and positive manner with ease. In most automotive engines, a mechanical means is provided in conjunction with the revolving crank shaft to provide a single indication for ignition timing purposes. Typically, when a fixed mark on a rotating member is directly under a fixed pointer on the engine block, the No. 1 piston is at top dead center (TDC). In a rotary engine, an analogous provision is made. With only one fixed point of reference being made available, it is difficult to set the distributor to accurately fire at 71/2.degree. before TDC or 3.degree. after TDC. In a modern engine scope tester, a lead is provided which is connected to the engine ignition system to sense the firing of the No. 1 spark plug. A timing light connected to the engine scope tester is coupled through an adjustable offset circuit so that the light can be fired before or after the actual firing of the No. 1 spark plug. The engine scope tester contains a meter indicating in distributor degrees the amount of this offset. The reading on the meter is twice that of the engine offset since the spark plugs fire once for every two engine revolutions and, consequently, the distributor rotates once for every two engine revolutions. Thus, if the manufacturer specifies a 10.degree. offset for spark plug firing, a 5.degree. distributor offset must be made. In such a case, the offset to the timing light is adjusted until the required offset is shown on the meter of the engine scope tester. With the engine running, the distributor is rotated to change the point at which the spark plugs fire. When the strobing timing light illuminates the fixed mark on the rotating member of the engine in alignment with the fixed pointer, the desired offset of 10.degree. has been attained accurately and the distributor is secured in that position. Appropriate means are included in a typical engine scope tester for providing both advance and retard adjustments through this timing light offset technique. The technique for accomplishing the offset forms no part of the present invention. The present invention relates only to the apparatus and technique for accurately calibrating the meter on the engine scope tester to the actual offset being set into the timing light as displayed in distributor degrees.